Diabetes can cause premature death and serious long-term complications. Monitoring the blood sugar level is one of the important steps to control the disease and lower the risks of complications. Currently, the most commercially successful continuous glucose concentration monitoring system is implantable CGMS™ from Minimed (Northridge, Calif.). However, there are several drawbacks about this enzyme glucose oxidase based electrochemical device. The sensing is irreversible due to the consumption of glucose, insensitive because of limited diffusion resulting from the affinity of cells and other biomolecules, and inaccurate due to its side production of hydrogen peroxide and other electrode active chemicals.
A microelectromechanical systems (MEMS) viscometric sensor device for continuous glucose monitoring, using Dextran and Con A as the sensing fluid, has previously been developed. For example, the commercial system, GlucOnline® (Roche Diagnostics GMBH) has a sensing fluid based on Dextran/Concanavalin A and allows for stable test signals and low-decay measurement. The sensing fluid is known to have significant drawbacks such as immunotoxicity, cytotoxicity and instability.
In general, boronic acids are biocompatible functional groups with low cytotoxicities and low immunogenicity. As shown in scheme 1, boronic acid binds reversibly to diols to form a cyclic boronate ester:

The binding causes photoelectron transfer or fluorescence resonance energy transfer or internal charge change that has been used to build fluorescent sensors. Asher, et al. have introduced the use of a polymerized crystalline colloidal array for calorimetric detection of glucose. See, Asher, S. A.; Alexeev, V. L.; Goponenko, A. V.; Sharma, A. C.; Lednev, I. K.; Wilcox, C. S.; Finegold, D. N. J. Am. Chem. Soc. 2003, 125, 3322-3329. Lei, et al. reported a swelling of the hydrogel due to the binding of glucose to the phenylborate group that was measured using a thin-film wireless pressure sensor. See, Lei, M.; Baldi, A.; Nuxoll, E.; Siegel, R. A.; Ziaie, B. Diabetes Technol. Therap. 2006, 8, 112-122. Arnold, et al. reported preliminary data from a conductimetric sensor with a boronic acid immobilized in a hydrogel, which was encapsulated in a bipolar ion exchange membrane impermeable to ions but freely permeable to glucose. See, Arnold, F. H.; Zheng, W. G.; Michaels, A. S. J. Membrane Sci. 2000, 167, 227-239. The change in ionic conductivity of the hydrogel resulting from the increase in ion concentration due to the binding of glucose to the boronic acid was measured with a pair of thin-film gold electrodes. However, there are intrinsic shortcomings with each type of those sensors. For example, fluorescence-based affinity sensors are inaccurate due to light intensity variations, the potential interference of other fluorescent biochemicals, and the requirement of relatively bulky and expensive optical instruments.
To address the drawbacks of the previous systems, a stable, biocompatible polymeric sensing fluid has been developed and is presently disclosed.